1. Field of the Invention
The present invention relates to the sequential excitation of several loads with the aid of an alternating current.
2. Discussion of the Background
This problem is posed especially in the electromagnetic systems for locating the position and orientation of an object at short range, such as those systems used for locating the position and the orientation of a helmet worn by a pilot, with respect to a three-axis reference system related to the pilot's cockpit, so as to allow the operation of certain instruments with the aid of the movements of the head pilot while leaving him complete freedom of movement.
One way, by an electromagnetic route, of locating the position and the orientation of an object, at short range, consists in sending at one reference point, successively along the three axes of an absolute three-axis reference system, electromagnetic fields at low frequency of the order of 10 KHz, in measuring, along the three axes of a relative three-axis reference system related to the object whose position and orientation it is desired to know, the components received from the successive electromagnetic fields sent along the three axes of the absolute three-axis reference system, and in deducing, from these measurements and from a preliminary cartography, the position and orientation of the relative three-axis reference system and hence of the object with respect to the absolute three-axis reference system. This way of doing it functions all the better when it is possible to generate successive electromagnetic fields in the precise directions of the three axes of the absolute three-axis reference system, that is to say when the successive emissions of these three electromagnetic fields are capable of being well decoupled.
The successive sending of these three electromagnetic fields is done with the aid of a triple antenna placed at the reference point and shaped into a cube with faces parallel to those of the absolute three-axis reference system. This triple antenna consists of three double orthogonal windings each arranged along two parallel faces of the cube and dimensioned so as to generate, for the same excitation current, the same electromagnetic field intensity outside the cube. Reception is done with the aid of a triple antenna of the same type carried by the object whose position and orientation it is desired to know, and shaped into a cube whose faces are parallel to those of the relative three-axis reference system.
The triple sending antenna constitutes, for the sender, a triple inductive load having a certain number of specific features.
Its three double windings, when they have the excitation current passing through them, develop, at their terminals, a high voltage which reaches about a hundred volts, pushing up the cost of the transistor multiplexer in the case where the transistors would have to withstand this voltage directly.
Moreover, these three double windings are not identical by reason of the constraints on coil forming along the faces of a cube, and exhibit different impedances which does not make it easy to maintain the same excitation current strength.
Moreover, these three windings are coupled by mutual inductance which promotes leakage currents.